A plate cylinder for use in a printing press is well known. Typically, a printing plate is secured to a plate cylinder by clamps located in an axially extending gap parallel to the longitudinal central axis of the plate cylinder. As known in the art, it is desirable to eliminate the gap. If the gap is eliminated, then the diameter of the plate cylinder can be reduced and the overall size of the printing press can thereby be reduced.
One known way of eliminating the gap is to use magnetic force to secure a magnetic (metal) printing plate to the plate cylinder. Typically, such a plate cylinder includes permanent magnets disposed within the plate cylinder. The permanent magnets provide a magnetic field with magnetic lines of flux passing through the magnetic printing plate. The magnetic force acting between the permanent magnets and the magnetic printing plate secure the magnetic printing plate to the plate cylinder.
One of the difficulties with using magnetic force to secure the magnetic printing plate to the plat cylinder is that it is difficult to remove the magnetic printing plate from the plate cylinder. This difficulty in removing the magnetic printing plate from the plate cylinder is because the magnetic force from the permanent magnets constantly act to hold the magnetic printing plate on the plate cylinder. This force must be overcome to remove the magnetic printing plate.